The rotary compressor generally comprises a shell, a compressing mechanism disposed in the shell, a driving mechanism for driving the compressing mechanism and so on. In order to ensure the normal operation of the compressor, there must be sufficient lubricating oil in the compressor. The lubricating oil level in the compressor should be higher than a lowest protection lubricating oil level. When the lubricating oil level in the compressor is lower than the lowest protection lubricating oil level, the compressor should be shut off.
A twin compressor system or even a multiple compressor system has been used widely. In this kind of twin or multiple compressor system, one or more of the compressors may be activated selectively and the others may be shut off, therefore lubricating oil would move in these compressors which may cause lubricating oil unbalance among compressors, even results in a situation that some compressors lack of lubricating oil.
In addition, lacking of lubricating oil may occur due to oil leakage in the compressor or oil leakage in the compressor system consisting of a single compressor or a plurality of compressors.
Furthermore, in the large refrigeration system having long pipeline and a great number of components, the lubricating oil may be unable to circulate back to the compressor in time, which causes lubricating oil shortage in the compressor.
As a result, the lubricating oil status (for example, height of lubricating oil level) in the compressor must be detected accurately to shut off the compressor timely and prevent the compressor from being damaged.